DENSITY

The same amount of two different liquids will have different weights because they have different masses.


 The liquids that weigh more (have a higher density) will sink below the liquids that weigh less (have a lower density).

 Density = Mass divided by Volume.

If the weight (or mass) of something increases but the volume stays the same, the density has to go up. 

The same goes for the small objects that you dropped into your density column.  The metal bolt is more dense than any of the liquids in the column and therefore sinks directly to the bottom.